QUANTITATION OF APOLIPOPROTEIN B-48 IN TRIACYLGLYCEROL-RICH LIPOPROTEINS BY A SPECIFIC ENZYME-LINKED-IMMUNOSORBENT-ASSAY

This paper describes the use of an antiserum, specific for apolipoprot ein (apo) B-48, in a competitive, enzyme-linked immunosorbent assay (E LISA) for apo B-48 in triacylglycerol-rich lipoprotein (TRL) fractions prepared from fasting and post-prandial plasma samples. Previously we showed the antiserum to act as an effective immunoblotting agent foll owing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-P AGE). Its use in this ELISA indicates that the antiserum recognises th e C-terminal region of the protein on the surface of lipoprotein parti cles. The ELISA had a sensitivity of less than 37 ng/ml and intra- and inter-assay coefficients of variation of 3.8% and 8.6%, respectively. There was no cross-reaction in the ELISA against serum albumin, ovalb umin, thyroglobulin, or apo B-100 (purified by immunoaffinity chromato graphy), and high lipid concentrations (as Intralipid) did not interfe re. A low density Lipoprotein fraction reacted in the ELISA but SDS-PA GE-Western blot analysis confirmed the presence, in the fraction, of a small amount of apo B-48, indicating the existence of low density die tary-derived lipoprotein particles. ELISA and SDS-PAGE-Western blot an alysis were used to measure apo B-48 in 12 series of postprandial samp les collected from 4 diabetic and 8 normal subjects, following test me als of varying fat content. The mean correlation between the two metho ds was r=0.74. The mean fasting concentration of apo B-48 in the TRL f ractions from 15 healthy men was 0.46 mu g/ml of plasma.